This application claims priority from EP 01304075.3 filed May 4, 2001, herein incorporated by reference.
The present invention relates generally to lithographic apparatus and more particularly to double exposure.
In general, a lithographic projection apparatus comprises a radiation system to supply a projection beam of radiation, a support structure to support patterning structure, the patterning structure serves to pattern the projection beam according to a desired pattern, a substrate table to hold a substrate, and a projection system to project the patterned beam onto a target portion of the substrate.
The term xe2x80x9cpatterning structurexe2x80x9d as here employed should be broadly interpreted as referring to structure or means that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term xe2x80x9clight valvexe2x80x9d can also be used in this context. Generally, the said pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning structure include:
A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
A programmable mirror array. One example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing piezoelectric actuation means. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors; in this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronic means. In both of the situations described hereabove, the patterning structure can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be gleaned, for example, from U.S. Pat. No. 5,296,891 and U.S. Pat. No. 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096, which are incorporated herein by reference. In the case of a programmable mirror array, the said support structure may be embodied as a frame or table, for example, which may be fixed or movable as required.
A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning structure as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning structure may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at one time; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatusxe2x80x94commonly referred to as a step-and-scan apparatusxe2x80x94each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4, incorporated herein by reference.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clensxe2x80x9d; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and PCT patent application WO 98/40791, incorporated herein by reference.
Lithographic projection apparatus and methods are known in which two masks and two exposures are used for the application of, for instance, dipole illumination in two orientations matched to critical features in said two orientations. Another example of such a two-mask two-exposure approach is the application of dipole illumination for printing dense features with small pitches, and the application of annular illumination for the printing of semi-dense to isolated features with pitches larger than the pitches of said dense features. As in the previous example, the two corresponding exposures are executed consecutively in order to obtain a combined exposure. Both examples of such xe2x80x9cdouble exposurexe2x80x9d applications have specific advantages. In the first example, the resolution in said two orientations can be improved over the resolution obtainable with, for instance, single exposure quadrupole illumination. In the second example, optical proximity correction methods can be chosen independently for the two exposures. This extra degree of freedom can be used to alleviate the problem of variation, as a function of pitch, of the dimension of printed features. Further information regarding such double exposure applications can be obtained, for example, from European patent applications EP 00308528.9 and EP 00310368.6, incorporated herein by reference. While such apparatus and methods benefit from improved performance compared to conventional apparatus and methods, a disadvantage is that they require twice as many exposures as conventional apparatus and methods, which consequently substantially halves the throughput.
In an aspect of at least one embodiment of the present invention, there is provided lithographic projection apparatus and methods that can combine two different mask exposures without substantially reducing throughput. Advantageously, the apparatus and methods allow two different patterns to be projected onto the substrate simultaneously, providing the performance benefits of double exposure methods without substantially increasing the throughput time of the process.
At least one embodiment of the present invention includes a lithographic projection apparatus comprising:
a radiation system for supplying a projection beam of radiation; a support structure for supporting a patterning structure, the patterning structure serving to pattern the projection beam according to a desired pattern; a substrate table for holding a substrate; a projection system for projecting the patterned beam onto a target portion of the substrate; a means for providing a supplementary projection beam of radiation; and wherein said support structure is further for supporting supplementary patterning structure, said supplementary patterning structure serving to pattern the supplementary projection beam according to a supplementary pattern which is different to the pattern of the patterning means and both patterned projection beams are projected simultaneously onto the substrate in overlapping registry with one another.
Furthermore, at least one embodiment of the present invention includes a device manufacturing method comprising: providing a substrate that is at least partially covered by a layer of radiation-sensitive material; providing a projection beam of radiation using a radiation system; supporting a patterning structure on a support structure and using it to endow the projection beam with a pattern in its cross-section; projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material; providing a supplementary projection beam of radiation; supporting a supplementary patterning structure on said support structure and using it to endow the supplementary projection beam with a pattern in its cross section that is different to the pattern of the patterning structure; and projecting the supplementary patterned beam onto the layer of radiation sensitive material simultaneously with the patterned beam.
For ease of reference we will, hereinafter, refer to the radiation system as xe2x80x9cfirst radiation systemxe2x80x9d and a supplementary radiation system as xe2x80x9csecond radiation system.xe2x80x9d Similarly, we will refer to the projection beam of radiation, the patterning structure, and the pattern as xe2x80x9cfirst projection beam of radiation,xe2x80x9d xe2x80x9cfirst patterning structure,xe2x80x9d and xe2x80x9cfirst pattern,xe2x80x9d respectively, and to the supplementary projection beam of radiation, the supplementary patterning structure, and the supplementary pattern as xe2x80x9csecond projection beam of radiation,xe2x80x9d xe2x80x9csecond patterning structure,xe2x80x9d and xe2x80x9csecond pattern,xe2x80x9d respectively.
Although specific reference may be made in this text to the use of the apparatus according to at least one embodiment of the present invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget portionxe2x80x9d, respectively.
In the present document, the terms xe2x80x9cradiationxe2x80x9d and xe2x80x9cbeamxe2x80x9d are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g having a wavelength in the range 5-20 nm), as well as particle beams, such as ion beams or electron beams.